The recent deliberate dissemination of anthrax spores has revealed significant gaps in our knowledge of anthrax pathogenesis. Macrophages play a key role in limiting anthrax infection by ingesting and eliminating the spores and vegetative bacilli. However, they also serve as a reservoir for replication and dissemination of the bacteria. We will use recently developed murine genetic models to clarify the role of the macrophages and dendritic cells (DCs) in anthrax pathogenesis. We will establish the time course of leukocyte trafficking to the lungs and draining mediastinal lymph nodes (MLNs) of mice infected with pulmonary anthrax, and we will identify the signals responsible for this recruitment. Previous work from our group has established that the monocyte chemoattractant protein (MCP) family of chemokines and their receptor, chemokine receptor 2 (CCR2), play pivotal roles in the migration of macrophages to sites of inflammation and that they are essential for host survival after infection with Mycobacterium tuberculosis. Unlike M. tuberculosis, a prominent feature of infection with Bacillus anthracis is the systemic effects produced by anthrax toxin acting on the macrophages. Thus, in the case of anthrax, it is unclear if impaired macrophage trafficking would be detrimental or perhaps even beneficial to the host. We will take advantage of our CCR2 mice to directly address this question in a model of pulmonary anthrax. DCs use another chemokine receptor CCR7 to traffic to draining lymph nodes (DLNs). To directly test whether CCR7, or its chemokine ligands secondary lymphoid chemokine (SLC), or Epstein-Barr ligand-1 chemokine, are involved in anthrax pathogenesis and host survival, we will take advantage of recently generated CCR7 mice. We will also attempt to establish a murine model of cutaneous anthrax infection. Progress in the understanding of cutaneous anthrax has been hampered by the lack of an adequate animal model. Once established, we will determine whether CCR2 and/or CCR7, known to regulate the trafficking of leukocytes through the skin, play a role in cutaneous anthrax. Completion of the specific aims of this proposal will establish the kinetics of leukocyte trafficking in pulmonary and cutaneous anthrax and will determine whether chemokines such as MCP-1 and SLC play important roles in phagocyte trafficking and host survival in anthrax infection. This information may provide a rationale for the use of chemokine/chemokine receptor antagonists in the treatment of anthrax.